1. Field of the Disclosure
The present disclosure relates to devices and methods for perforating a well having high wellbore fluid pressure.
2. Description of the Related Art
Hydrocarbons, such as oil and gas, are produced from cased wellbores intersecting one or more hydrocarbon reservoirs in a formation. These hydrocarbons flow into the wellbore through perforations in the cased wellbore. Perforations are usually made using a perforating gun loaded with shaped charges. The gun is lowered into the wellbore on electric wireline, slickline, tubing, coiled tubing, or other conveyance device until it is adjacent the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow through the perforations and into a production string.
In some of the more recent hydrocarbon exploration and recovery activity, well owners have encountered relatively high fluid pressures in the drilled wellbores; e.g., fluid pressures approaching and exceeding 25,000 PSI. As will be seen, such pressures can be problematic for conventional perforating gun configurations, one of which is shown in FIG. 1. In FIG. 1, there is shown a conventional perforating gun 10 that includes a charge strip or tube 12 positioned in a carrier tube 14. Fixed within the charge tube 12 are shaped charges 18. A detonator cord 16 runs through suitable bores to the shaped charges 18. Connector subs such as a top sub 22, intermediate subs 24, and a bottom sub 26 are used to interconnect the various components making up the gun 10, connect together two or more guns 10, seal the interior 28 of the gun 10 and/or provide a connection point 30 to the conveyance device used to run the gun 10 or gun train into the wellbore.
Conventionally, the gun 10 is a sealed tool, which means that the interior 28 of the gun 10 is at approximately atmospheric pressure, or at least at a pressure substantially lower than the pressure of the wellbore fluid surrounding the gun 10. Typically, the carrier tube 14 is formed of steel or steel alloy, which exhibits suitable compressive strength at pressures below 25,000 PSI. That is, a conventional steel carrier tube 14 resists crushing or catastrophic deformation at pressure below 25,000 PSI. However, for pressures approaching 25,000 PSI, the carrier tube 14 typically incorporates exotic and expensive steel alloys and/or utilizes substantially thick walls. In some cases, the wall thickness required to resist crushing is impractical because it would unduly restrict the space for the shaped charges 18. In other cases, the cost of the perforating gun can become prohibitive.
Prior art gun configurations have utilized non-steel components. For example, U.S. Pat. No. 6,865,792 relates to methods for making a perforating gun that involves, in part, forming a carrier tube having multiple layers. These methods, however, appear to be primarily directed to fabricating a carrier tube at low cost. U.S. Pat. No. 5,829,538 teaches a perforating gun having charge holders and explosive charges that are formed of materials that disintegrate upon detonation of the explosive charges. U.S. Pat. No. 6,422,148 teaches a perforating gun assembly that includes at least one component that is constructed from a composite material and that is impermeable to wellbore fluids. The composite component is designed to shatter into small pieces upon detonation of the perforating gun. Thus, conventional gun arrangements using non-metal components have not addressed the difficulties presented in relatively high-pressure wellbore situations.
The present disclosure addresses these and other drawbacks of the prior art.